Process for treating solid surface and substrate surface

ABSTRACT

Ruthenium, osmium and their oxides can be etched simply and rapidly by supplying an atomic oxygen-donating gas, typically ozone, to the aforementioned metals and their oxides through catalysis between the metals and their reactors and application of the catalysis not only to the etching but also to chamber cleaning ensures stable operation of reactors and production of high quality devices.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a process for treating thesurface of a solid containing ruthenium, osmium or their oxide byetching. Furthermore, the present invention relates to a process forproducing a semiconductor device, particularly to a process for etchingtreatment and cleaning treatment of said metal or its oxide formed abovea substrate and also relates to a process for cleaning a CVD reactor oran etching reactor used in the foregoing processes.

[0002] With recent higher integration of semiconductor devices, deviceswith memory cells such as DRAM, etc. will have more and more complicatedspatial structures to ensure a condenser capacitance. Consequently,number of steps for device production is increased and a margin for thinfilm formation and processing is narrowed, thereby increasing theproduction cost and lowering the yield. Thus, it is essential for anincrease in the condenser capacitance to use novel high-dielectricmaterials to simplify the structure.

[0003] Double oxides such as BaSrTiO₃ are now under study as such highdielectric materials. It is necessary to conduct high temperatureannealing in an oxygen atmosphere during the formation of these oxides.However, in case of using Si as a condenser lower electrode material, itis hard to suppress an increase in the resistance due to oxidationduring the oxygen annealing, and thus it is necessary to use scarcelyoxidizable novel materials or materials which have a goodelectroconductivity even if oxidized.

[0004] As electrode materials which can satisfy these conditions, forexample, ruthenium and ruthenium oxide are now under study.

[0005] As a process suitable for forming these electrode materials, aCVD (chemical vapor deposition) process has been proposed, which canproduce a thin film of high purity and distinguished crystallinity witha good thin film depositability onto a substrate relative to thephysical vapor deposition.

[0006] Processes for forming a thin film of ruthenium or ruthenium oxideby MO-CVD using specific organic feed gases are disclosed, for example,in JP-A-6-283438 and JP-A-9-246214.

[0007] As to processes for forming a thin film of ruthenium or rutheniumoxide by etching, on the other hand, a process for producing asemiconductor device, which comprises a step of plasma etching using agas mixture comprising at least one member selected from the groupconsisting of a halogen gas comprising at least one of fluorine gas, achlorine gas and an iodine gas and hydrogen halides, and an oxygen gasor an ozone gas is disclosed, for example, in JP-A-8-78396.

[0008] Furthermore, a process for obtaining pure ruthenium tetraoxide byreaction of ruthenium with ozone at room temperature is disclosed byRainer Loessberg and Wrich Mueller in Zeitschrift fuer Naturforschung,Section B, Chemical Sciences, vol. 16B, No. 3, 1981, pp 395.

[0009] Still furthermore, as to a technique of removing rutheniumresidues, a wet cleaning process using a cleaning solution comprisingperiodic acid and nitric acid is disclosed in Japanese PatentApplication No. 11-245143.

BRIEF SUMMARY OF THE INVENTION

[0010] An object of the present invention is to improve said prior artprocesses and provide a process for treating ruthenium, osmium or theiroxides simply and rapidly by etching without any damages to wafers ordevices.

[0011] The present invention provides a process for treating a solidsurface, characterized by treating the surface of a solid comprising atleast one member selected from the group consisting of ruthenium,ruthenium oxide, osmium and osmium oxide by etching by supplying a gascomprising an atomic oxygen-donating gas to the solid surface.

[0012] Furthermore, the present invention provides a process fortreating a substrate surface, a process for cleaning a substrate, aprocess for cleaning a reactor for producing a semiconductor and aprocess for producing a semiconductor device, utilizing said process fortreating the solid surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a graph showing vapor pressure curves of rutheniumcompounds.

[0014]FIGS. 2A to 2C are graphs showing relationships betweendifferences in Gibbs' free energy and reaction temperatures in rutheniumoxidation reactions.

[0015]FIGS. 3A to 3C are cross-sectional views showing steps ofproducing a semiconductor device according to Example 1.

[0016]FIG. 4 is a schematic view of an etching reactor used in Example1.

[0017]FIG. 5 is a graph showing relationships between ruthenium etchingrates and treatment temperatures.

[0018]FIG. 6 shows an example of quadruple mass spectrometry (QMS) ofreaction products from reactions between ruthenium and ozone.

[0019]FIG. 7 is a graph showing relationships between thermaldecomposition of ozone and existent ratio of ozone on wafers.

[0020]FIG. 8 is a schematic view showing reaction mechanisms betweenruthenium and ozone.

[0021]FIG. 9 is a block diagram showing a sequence of etching treatmentsteps according to Example 1.

[0022]FIGS. 10A and 10B are schematic views showing an ozone cleaningeffect on ruthenium-contaminated wafers according to Example 2.

[0023]FIG. 11 is a schematic view showing an ozone cleaning reactoraccording to Example 2.

[0024]FIG. 12 is a schematic view showing cleaning of a CVD reactoraccording to Example 3.

[0025]FIG. 13 is a graph showing results of QMS reaction analysisrelating to detection of a cleaning end point.

[0026]FIG. 14 is a graph showing changes in particle counts in CVDreactor by cleaning.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be described below in detail, wheredescription will be made on the essential points of the presentinvention not disclosed in said prior art.

[0028] Processes for etching ruthenium or ruthenium oxide disclosed insaid prior art are based on plasma etching reactions using ion-assistreactions, where use of a plasma makes it difficult to prevent anetching target from damaging and also increases a reactor cost. Thus, ithas been keenly desired to provide a simple etching process without anydamages to substrates.

[0029] Likewise in the conventional processes for removing rutheniumresidues or contaminations, removal based on the plasma etchingreactions gives damages to substrates and the wet cleaning processrequires steps of rinsing and drying. Thus, it has been also desired toprovide a simple process for cleaning ruthenium residues orcontaminations without any damages to substrates.

[0030] In case of producing a semiconductor device such as DRAM, etc.using a CVD reactor for forming a thin film of ruthenium or rutheniumoxide as novel materials or using an etching reactor for forming apattern by etching the thin film, on the other hand, it has been desiredin the semiconductor industry to establish a process for removingreaction products including ruthenium as accumulated or deposited in thereactor chambers or pipes by cleaning to reduce dust emission from thereactors and produce semiconductor devices in good yield, thereby makingready for the next step.

[0031] Generally, in case of etching ruthenium or osmium, it is possibleto remove said metal by converting it to a metal compound with a highervapor pressure (e.g. ruthenium compound or osmium compound).

[0032] For example, temperature dependency of vapor pressures of typicalruthenium compounds is shown in FIG. 1. As is evident from FIG. 1, RuO₄is an oxide having the highest vapor pressure at 200° C. or lowertemperatures. It can be seen therefrom that in case of using rutheniumin a semiconductor device a relatively low etching temperature isdesirable in the etching treatment step from the viewpoint of thermalbudget and throughput, and it is actually preferable to form RuO₄ with ahigher vapor pressure characteristic in a temperature range of nothigher than 200° C.

[0033] Furthermore, formation of a metal oxide has a great merit as tothe reactor structure and its maintenance. That is, in case of formingand utilizing a metal halide, a highly corrosive halogen-based gas isused and thus a complete safety means must be provided on the reactor,the treatment process, etc.

[0034] Reaction of forming RuO₄ from ruthenium will be described below:

[0035] Studies have been made from a thermodynamic viewpoint on aprocess for forming said oxide by non-plasma-based reaction withoutusing high energy such as plasma, etc. to establish a simple etchingprocess with less damages to an etching target.

[0036]FIGS. 2A to 2C show relationships between differences in Gibbs'free energy (ΔG) and reaction temperatures in the reaction of formingRuO₄ from Ru.

[0037] Relationships between ΔG and reaction equilibrium constant (K)can be given by the following equation:

K∞exp(−ΔG/RT)

[0038] where R is a gas constant and T is an absolute temperature.

[0039] This equation means that with increasing difference in Gibbs'free energy (ΔG) towards the plus side oxidation reaction of rutheniumless proceeds, whereas with increasing ΔG towards the minus side theoxidation reaction is promoted.

[0040] It is evident from the results of FIGS. 2A to 2C that in case ofreaction of ruthenium by ozone or atomic oxygen the reaction proceedsmore easily because the difference in Gibbs' free energy (ΔG) to formRuO₄ is larger towards the minus side, and even if RuO₂ happens to formin the course of reaction. RuO₂ further reacts with ozone or atomicoxygen to form RuO₄.

[0041] As is obvious from FIG. 2C, even if the difference in Gibbs' freeenergy (ΔG) to form RuO₄ is on the minus side in the reaction of Ru withO₂, on the other hand, its absolute value is far less than those in caseof ozone or atomic oxygen, the reaction is hard to proceed. Once RuO₂ isformed in the reaction with O₂, conversion of RuO₂ to RuO₄ hardlyproceeds.

[0042] It is obvious from these test results, ruthenium or rutheniumoxide must be made to react with ozone or atomic oxygen to form RuO₄therefrom. The foregoing reaction mechanism is true not only ofruthenium but also of osmium.

[0043] When a very small amount of a halogen gas or a hydrogen halidegas is added to the ozone gas or atomic oxygen gas to cause halogenationreaction of ruthenium, formation of RuO₂, which is relatively stable andhard to undergo further reaction, can be suppressed. By adding areductive gas thereto, the formed RuO₂ can be reduced to Ru.

[0044] Based on the foregoing reaction behavior of ruthenium, thepresent invention has been established to provide a process for treatingthe surface of a solid comprising at least one member selected from thegroup consisting of ruthenium, ruthenium oxide, osmium and osmium oxideby etching, where the etching treatment of the solid surface can beattained by supplying an atomic oxygen-donating gas to the solidsurface.

[0045] Furthermore, by conducting the same treatment as described aboveto a substrate surface with a film of said metal or metal oxide asformed thereon, etching treatment of the substrate surface can beattained.

[0046] Still furthermore, by treating a substrate with a film orparticles comprising at least one member selected from the groupconsisting of ruthenium, ruthenium oxide, osmium and osmium oxide, asdeposited thereon, according to the same process as described above,cleaning treatment of the substrate can be attained.

[0047] Still furthermore, in cleaning treatment of a CVD reactor forforming a film comprising at least one of said members on a substrate orin cleaning treatment of an etching reactor for forming a pattern byetching said film, reaction products including ruthenium or osmium asaccumulated or deposited at least in the chambers of these reactors oron the surfaces of pipings can be likewise removed.

[0048] In the present invention, the atomic oxygen-donating gasincludes, for example, at least a gas selected from the group consistingof ozone, oxygen halide, nitrogen oxide and atomic oxygen and can beused in the etching treatment upon admixing the gas with a halogen gas,a hydrogen halide gas or a reductive gas or further with at least a gasselected from the group consisting of fluorine, chlorine, bromine,chorine fluoride, hydrogen fluoride, hydrogen chloride, hydrogenbromide, hydrogen, carbon monoxide, ammonia and phosphorus hydride.

[0049] These treatment reactions are non-plasma etching treatments andare carried out so as not to form an ion sheath on or above the surfaceof a solid or substrate.

[0050] The foregoing reactions of the present invention can be attainedat a solid or substrate surface temperature of 20° to 350° C.,preferably 40° to 200° C., more preferably 40° to 180° C.

[0051] The present invention will be described more in detail below,referring to varieties of processes as envisaged according to thepresent invention, to each of which the aforementioned treatmentconditions can be applied.

[0052] [A] A process for treating a substrate surface, which comprises(1) a step of transferring a substrate to a treatment chamber from atransfer chamber, (2) a step of adjusting the temperature of thesubstrate, (3) a step of supplying a gas comprising an atomicoxygen-donating gas into the treatment chamber, (4) a step of treatingthe substrate surface in the treatment chamber by etching, and (5) astep of transferring the treated substrate to the transfer chamber fromthe treatment chamber, where a film comprising at least one memberselected from the group consisting of ruthenium, ruthenium oxide, osmiumand osmium oxide, formed above the substrate in the step (3), is etchedin the step (4).

[0053] [B] A process for cleaning a substrate, which comprises (1) astep of transferring a substrate to a treatment chamber from a transferchamber, (2) a step of adjusting the temperature of the substrate, (3) astep of supplying a gas comprising an atomic oxygen-donating gas intothe treatment chamber, (4) a step of cleaning the substrate in thetreatment chamber, and (5) a step of transferring the cleaned substrateto the treatment chamber to the transfer chamber, where a film orparticles comprising at least one member selected from the groupconsisting of ruthenium, ruthenium oxide, osmium and osmium oxide,deposited above the substrate in the step (3) is removed in the step(4).

[0054] [C] A process for cleaning a substrate, which comprises (1) astep of transferring a substrate to a treatment chamber from a transferchamber, (2) a step of adjusting the temperature of the substrate, (3) astep of supplying a gas comprising an atomic oxygen-donating gas intothe treatment chamber, (4) a step of cleaning the substrate in thetreatment chamber, and (5) a step of transferring the cleaned substrateto the transfer chamber from the treatment chamber, where a film orparticles comprising at least one member selected from the groupconsisting of ruthenium, ruthenium oxide, osmium and osmium oxide,deposited at least at edges or on the backside of the substrate in thestep (3) is removed in the step (4).

[0055] [D] A process for cleaning a reactor for producing asemiconductor device, the reactor comprising a treatment chamber fortreating a substrate, which comprises removing at least one ofruthenium, osmium and a reaction product comprising at least one ofruthenium and osmium accumulated or deposited on the surfaces of membersin the treatment chamber by a gas comprising an atomic oxygen-donatinggas.

[0056] [E] A process for cleaning a reactor for producing asemiconductor device, the reactor comprising a treatment chamber fortreating a substrate, which comprises (1) a step of transferring asubstrate into the treatment chamber, (2) a step of treating thesubstrate, (3) a step of transferring the treated substrate from thetreatment chamber, and (4) a step of cleaning to remove productsaccumulated or deposited on the surfaces of members in the treatmentchamber after the transfer of the substrate, where the product is atleast one of ruthenium, osmium and a reaction product comprising atleast one of ruthenium and osmium, the product is removed by a gascomprising an atomic oxygen-donating gas, and the step (4) is carriedout after desired repetitions of the step (2).

[0057] [F] A process for producing a semiconductor device, whichcomprises (1) a step of forming a film comprising at least one memberselected from the group consisting of ruthenium, ruthenium oxide, osmiumand osmium oxide above a substrate placed in a first treatment chamber,(2) a step of forming a circuit pattern on the film above the substrateplaced in a second treatment chamber, and (3) a step of cleaning toremove a reaction product including the film, accumulated or depositedon the surfaces of members in at least one of the first treatmentchamber and the second treatment chamber, where step (3) of cleaning iscarried out by a gas comprising an atomic oxygen-donating gas.

[0058] The present invention will be described in detail below,referring to drawings.

[0059] “Semiconductor device” herein referred to means semiconductordevices such as memory elements, etc. formed on a silicon substrate, TFTelement for liquid crystal display formed on a quartz or glasssubstrate, and other devices in general, form on substrates. “Substrate”herein referred to means semiconductor substrates of silicon, etc. forforming a semiconductor device on their surfaces, insulating substratesand their composite substrates, but is not limited thereto.

[0060] “Non-plasma etching treatment” herein referred to does not meanan etching treatment using an ion sputtering action or an etchingtreatment using an ion-assist reaction such as reactive ion etching,where reaction by ions acceleratedly injected onto a target surface isdominant, but means an etching treatment using chemical reactionsbetween constituent molecules themselves of an etching gas and a targetsurface, which take place in a high level energy state brought aboutmainly due to the external heat.

[0061] Thus, it is so characteristic of the present invention that noion sheath is formed on or above the surface of a solid, a substrate orin the reactor in contrast to its formation so often observable in caseof the plasma etching.

[0062] Detailed description will be made below as to “ion sheath”. “Ionsheath” means a space charge layer, which is formed by contact of plasmawith a solid. As the plasma electron temperature is generally higherthan the ion temperature, light electrons are injected into the solidsurface at a high speed, so that the solid will have a negativepotential relative to the plasma. Thus, the injected electrons aremoderated or reflected in positions near the solid surface to form anion-excess space charge layer, i.e. ion sheath. When chemical reactionstake place in a thermal atmosphere, as will be hereinafter described, onthe other hand, there will be no plasma near the solid surface and thusno ion sheath will be formed.

[0063] However, a remote plasma treatment, which comprises transportingto a target solid surface a plasma gas existing in a space isolated fromthe target solid through a pipe, forms no ion sheath near the targetsolid surface and thus is included in the non-plasma treatment.

[0064] “Ruthenium oxide” means any one of RuO, RuO₂, RuO₃ and RuO₄, and“osmium oxide” means any one of OsO, Os₂O₃, OsO₂, OsO₃ and OsO₄.

Example 1

[0065] An embodiment of etching a ruthenium film formed above asubstrate, in case of a semiconductor device is given below, and asequence of etching steps is shown in FIGS. 3A to 3C.

[0066]FIG. 3A is a cross-sectional view of a semiconductor device, wherea silicon oxide film 32 is formed on a silicon wafer (silicon substrate)31 by well known thermal oxide film formation and then a pattern isformed on the silicon oxide film 32 by anisotropic dry etching.

[0067] Then, as shown in FIG. 3B, a ruthenium film 33 is formed on thesilicon oxide film 32 by ordinary CVD and then a portion of theruthenium film 33 is removed by ordinary dry etching, as shown in FIG.3C, so as to bring the silicon dioxide film 32 and the ruthenium film toan equal surface level.

[0068] In this manner, the ruthenium film 33 is filled in the holesformed by the anisotropic dry etching to complete plugs 33 consisting ofruthenium.

[0069]FIG. 4 is a schematic view showing an etching reactor for removinga portion of the ruthenium film 33.

[0070] The etching reactor comprises a treatment chamber 41 for mainlyconducting etching treatment, a wafer 42, a suspect heater 43 forheating the wafer 42 and a shower head 44 for supplying a gas. Thetreatment chamber 41 is provided with a pipe 49 connected to an ozonizer45 s for supplying ozone, an oxygen supplier 46 s for forming ozone, anitrogen supplier 47 s and another nitrogen supplier 48 s for adjustingan ozone concentration through valves 45 v, 46 v, 47 v and 48 v,respectively, and is further provided with a pumping pipe 49 connectedto a conductance control valve 410 for adjusting the pressure in thetreatment chamber 41, a vacuum pump 411 and a facily 112 for removingozone, etc., successively. Furthermore, the treatment chamber 41 isconnected to a transfer chamber with a transfer arm 413.

[0071] At first, etching conditions for the ruthenium film 33 must bedetermined.

[0072] Results of etching characteristics of the ruthenium film 33 by anozone-containing gas investigated in the reactor shown in FIG. 4 will beexplained below:

[0073]FIG. 5 is a graph showing the temperature dependency of etchingrate when the ruthenium film 33 formed by CVD was etched, for example,by an ozone gas. Etching was carried out at an ozone concentration of 5%and a gas flow rate of 10 slm under pressure each of 100 Torr and 700Torr in the treatment chamber. Ozone was generated by an ozonizer undersilent discharge.

[0074] It was found that the ruthenium film was etched by ozone at atreatment temperature ranging from 200° to 350° C. and a maximum etchingrate was obtained at about 100° C. The maximum etching rate was severaltimes higher than that of so far known ruthenium film 33. The etchingrate was determined by characteristic X-ray intensities measured byX-ray fluorescent analysis.

[0075] Etching reaction mechanism between the ruthenium film 33 and theozone gas will be explained below:

[0076]FIG. 6 shows a mass spectrum graph of reaction products frometching treatment of the ruthenium film 33 in the etching reactor asshown in FIG. 4, determined by QMS (quadruple mass spectrometry) in thepipe 49. As is clear from the results, Ru, RuO₂, RuO₃ and RuO₄ weredetected as reaction products, among which the reaction product havingthe highest spectral intensity was found to be RuO₄ and the mainreaction product from the reaction between the ruthenium film 33 and theozone gas was also found to be RuO₄. It seems that Ru, RuO, RuO₂ andRuO₃ resulted from decomposition of RuO₄ in the ionization chamber ofQMS.

[0077] In the formation of RuO₄ from simple ruthenium metal, it isnecessary to decompose the ozone gas as a reactant gas.

[0078]FIG. 7 is a graph showing changes in existent rate of ozone (valueobtained by subtracting a percent ozone deposition from 100) with time,when the ozone gas supplied into the treatment chamber was thermallydecomposed, where FIG. 7 was based on calculation results of data givenin Hidetoshi Sugimura: Basics and Application of Ozone, page 58,published by Korin (1996).

[0079] In view of the flow rate of the ozone gas in the etching chambershown in FIG. 4, it would take not more than a few second before theozone supplied into the treatment chamber 41 was brought into contactwith the heated ruthenium, and thus the ozone would be brought intocontact with the ruthenium film without any substantial thermaldecomposition at a treatment temperature of not more than 200° C.

[0080] Thus, it seems that the ozone was decomposed by other energy thanheat in the temperature zone showing the maximum etching rate ofruthenium as shown in FIG. 5, contributing to the reaction withruthenium. The treatment temperature was measured by a well known means,for example, a thermocouple mounted on the surface of the wafer 42including the ruthenium film 33.

[0081] It is reported in the aforementioned “Basics and Application ofOzone” or “Ozone decomposition catalyst with a broadening applicationfield” (JETI, Vol. 39, No. 11, 1991) that the ozone can be decomposed bycatalysis of platinum, etc. Ruthenium, on the other hand, belongs to theplatinum group and in view of the aforementioned catalysis it seems thatthe ozone can be decomposed also by catalysis of ruthenium, giving goodgrounds for RuO₄ formation reaction to take place even at low treatmenttemperatures such as about 100° C.

[0082] It can be seen from the foregoing that reactions betweenruthenium and ozone can proceed according to the reaction mechanismsshown in FIG. 8 or reaction equations given in the following Table 1.RuO is very unstable and thus seems to be converted to more stable RuO₄through reactions with ozone. TABLE 1 RuO₄ formation process Reactionprocess Reaction equation {circle over (1)} Supply of O₃ onto Ru surface{circle over (2)} Adsorption of O₃ onto Ru surface O₃ → O_(3 ads){circle over (3)} O₃ decomposition O_(3 ads) → O₂ + O_(ads) {circle over(4)} Reaction between Ru and 0 Ru + O_(ads) → RuO_(ads) {circle over(5)} Formation of RuO₄ from RuO and O₃ RuO + O₃ → RuO_(4 ads) {circleover (6)} Desorption of RuO₄ RuO_(4 ads) → RuO₄ ↑

[0083] Reasons why the etching rate of ruthenium by ozone starts tolower from the high temperature zone of about 100° C. as shown in FIG. 5will be explained below:

[0084] From results of measurement of a ratio of RuO₂ to Ru by weight atthe respective treatment temperatures by well known analytical methodXPS it was found that the weight of RuO₂ existent on the ruthenium filmsurface was increased with increasing treatment temperature. In FIG. 5,the etching rate obtained by exposing a RuO₂ film formed by sputteringmerely to an ozone gas is also plotted in FIG. 5 (mark x), from which itis evident that the RuO₂ film was substantially not etched by simpleozone.

[0085] From the foregoing results it can been seen that at hightreatment temperatures the formation reaction of stoichiometricallystable RuO₂ is more dominant than the formation reaction of RuO₄ shownby reaction equation {circumflex over (5)} of Table 1 and the RuO₂formed on the surface will inhibit the successive reactions. Reasons whyRuO₂ is substantially not etched seem to be that RuO₂ per se has nocatalysis on decomposition of ozone, RuO₂ is thermodynamically stableand the difference in Gibbs' free energy of reaction (ΔG) approacheszero or the plus side from the minus side with increasing temperaturesas shown in FIGS. 2A to 2C.

[0086] In view of the aforementioned reaction mechanisms betweenruthenium and ozone, it is important in the removal by etching of aportion of the ruthenium film 33 formed on the substrate 31 shown inFIG. 3B that (1) an etching rate ensuring the necessary throughput forproducing a semiconductor device must be obtained, (2) the surface ofthe ruthenium film 33 must not be modified (oxidized) and (3) uniformetching must be obtained on the surface of the wafer 31.

[0087] From the foregoing results of investigation, it has been foundthat etching treatment of the ruthenium film 33 can be carried out withozone at a treatment temperature ranging from 20° to 350° C. However, toobtain an etching rate ensuring a production throughput and suppressoxidation on the surface of the ruthenium film 33, the treatmenttemperature is preferably restricted to a range of 40°-200° C. Toconduct uniform etching of the surface of the wafer 31, an ozone gasmust be uniformly supplied onto the surface in the treatment chamber 41when the reaction is in a diffusion rate-determining step or thetreatment temperature must be made uniform over the surface of the wafer31 when the reaction is in a reaction rate-determining or desorptionrate-determining step.

[0088] Etching was conducted at the treatment temperature of 60° C.,which is in a desorption rate-determining step, in the reactor shown inFIG. 4, whose a treatment sequence is shown in FIG. 9.

[0089] According to the treatment sequence of FIG. 9, a portion of theruthenium film 33 formed on the substrate wafer 31 was carried out atthe treatment temperature of 60° C. As a result, ruthenium film plugs 33were formed, as shown in FIG. 32. The uniformness on the surface of thewafer 31 obtained in that etching rate was found to be about ±5%, whichwas on a practically trouble-free level.

[0090] In this embodiment, etching of the ruthenium film 33 could becarried out at a relatively high rate by using on ozone gas, and noplasma is used in the reactions, giving no damages to the substrate 31.Damages to members of etching reactor, for example, corrosion, etc. ofmetallic parts, could be suppressed by using an ozone gas.

[0091] In the foregoing embodiment, ozone was used as an etching gas,but use of oxygen halide, nitrogen oxide and atomic oxygen had the sameeffect as above. The same effect was also obtained by introducing anoxygen or nitrogen oxide gas excited by ultraviolet rays or plasmabeforehand.

[0092] In the foregoing embodiment, a gas mixture of oxygen and nitrogenfurther containing a few % of ozone was used, but even further additionof a halogen gas and a hydrogen halide such as fluorine, chlorine,bromine, chlorine fluoride, hydrogen fluoride, hydrogen chloride,hydrogen bromide, etc. thereto had the same effect.

[0093] In this embodiment, addition of a reductive gas such as hydrogen,carbon monoxide, ammonia, phosphorus hydride, etc. in place of a few %of ozone to the gas mixture of oxygen and nitrogen also had the sameeffect.

[0094] The foregoing results were also true of a ruthenium oxide film,an osmium film and an osmium oxide film, where the same effect as incase of the ruthenium film could be obtained.

Example 2

[0095] Ruthenium film or its particles deposited on the wafer backsideor edges of the wafer upside was removed.

[0096] For example, in a CVD reactor for a ruthenium film, a wafer isplaced on a heater and heated, where the heater temperature is at afilm-forming temperature or higher, and consequently the ruthenium filmis formed not only on the wafer, but also sometimes on the heaterbesides the wafer. Repetition of the CVD film formation sometimes causesdeposition of a ruthenium film on the wafer backside. To preventformation of a ruthenium film on the edges of the wafer upside, theedges are sometimes brought into contact with a shadow ring forpreventing supplying of a film-forming gas to the edges, but a rutheniumfilm is formed even on the shadow ring due to as high a shadow ringtemperature as the heater temperature.

[0097] When the wafer with the ruthenium film deposited on the waferbackside or wafer upside edges is subjected to another treatment in asuccessive reactor, the ruthenium film deposited on the wafer backsideor wafer upside edges per se causes contamination of the successivereactor, giving an adverse effect on the performance of ultimatesemiconductor devices.

[0098] Thus, a cleaning process for removing the ruthenium film orparticles deposited on the wafer backside or wafer upside edges afterthe CVD film formation or etching is indispensable for preventing anyruthenium film contamination from other reactors.

[0099] In FIG. 10A, a device pattern 52 is formed on the upside of awafer 51, where upside edges 53 and the backside of the wafer 51 arecontaminated with a ruthenium film 54 or ruthenium particles 55. Areaswith a ruthenium contamination rate (intensity detected by fluorescentX-ray) of not less than 10¹³ atoms/cm² on the upside edges 53 and thebackside of the wafer 51, measured by well known total reflectionfluorescent X-ray are indicated by black areas.

[0100]FIG. 10B shows cleaning effect of ozone on the wafer 51, whereother surfaces of the wafer 51 than the backside and upside edges 53 ofthe wafer 51 are coated with a resist before exposing the wafer 31 toozone, so that the ruthenium film formed on the pattern 52 of the devicemay not be etched. The surface layer each on the backside and upsideedges 53 of the wafer 51 is made from a silicon oxide film.

[0101] Ozone etching selectivity between ruthenium and ozone wasinvestigated by changing the treatment temperature from room temperatureto 300° C. As a result, it was found that the etching rate of rutheniumwas higher than that of the resist at temperatures of not more thanabout 180° C., whereas the etching rate of the resist was higher above180° C. As already shown in Example 1, it seems that the ozone isdecomposed by catalysis of ruthenium, promoting the etching at lowtemperatures, whereas the resist itself has no catalysis. This is asignificant difference as mentioned above.

[0102] Thus, the device pattern 52 can be protected from etching bycovering the device pattern-formed area 52 with a resist and conductingetching at a temperature of not ore than 180° C. To effectively removeruthenium contaminants in view of treatment throughput, the treatmenttemperature is desirably not less than about 40° C.

[0103]FIG. 10B shows results of cleaning the wafer 51 shown in FIG. 10Aunder the aforementioned conditions. As is obvious therefrom, theruthenium-contaminated areas 55 have been removed from the upside edges53 and the backside of the wafer 51.

[0104]FIG. 11 is a schematic view of a ruthenium dry cleaning reactorinto which the aforementioned results of investigation are incorporated.This example presupposes a hot wall type cleaning reactor of batchsystem, which comprises a treatment chamber 111 with a heating means,directed mainly to a cleaning treatment, wafers 112, quartz wafersupports 113 for supporting wafers and gas diffusers 114. The treatmentchamber 114 is provided with a pipe 119 connected to an ozonizer 115 sfor supplying ozone, an oxygen supplier 116 s necessary for formingozone, a nitrogen supplier 117 s, and another nitrogen supplier 118 sfor adjusting the ozone concentration through respective valves 115 v,116 v, 117 v and 118 v, and also provided with a pumping pipe 119connected to a conductance control valve 1110 for adjusting the pressurein the treatment chamber 114 and a vacuum pump 1111. Furthermore, thetreatment chamber 111 is provided at both sides with transfer chambers1113 a and b with arms 1114 a and b for transporting the wafers 112,operated by transfer robots 1115 a and b, through gate valves 1112 a andb, respectively.

[0105] The cleaning reactor may be connected to an etching reactor or aCVD reactor through the transfer chamber 1113.

[0106] Cleaning treatment was carried out in the following manner:

[0107] The wafer 112 with the device pattern formed thereon and coatedwith a resist (whose ruthenium contamination rate being substantiallythe same as that of FIG. 10A) was transferred into the treatment chamber111 and treated at 100° C. The temperature was selected in view of ahigher etching rate of ruthenium, a higher selectivity ratio ofruthenium to resist (about 100) and also assurances of protecting eventhe resist against modification. The wafer 112 was mounted on thesupports 113 in a facedown mode of turning the resist-formed sidedownward so as to prevent contact of the wafer backside and the upsideedges with reactor members as much as possible.

[0108] Pressure was 700 Torr with a flow rate of 10 slm, an ozoneconcentration of 10% and a cleaning time of 3 minutes.

[0109] The treated wafer 112 was transferred from the treatment chamber111 and subjected to measurement ruthenium contamination rates of thetreated wafer by total reflection fluorescent X-ray. The results showedthe same as in FIG. 10B. That is, the existent ruthenium contaminationrate on the upside edges and the backside of the treated wafer 112 wasbelow the detection limit of the detector. Furthermore, the existentrate on the wafer backside was found to be not more than 5×10¹⁰atoms/cm² by measurement using a well known ICP-Mass spectrometer. Fromthese results it can be seen that ruthenium contaminants deposited onthe unwanted parts of the wafer 112 could be removed by theaforementioned cleaning treatment.

[0110] In this embodiment, neither rinsing step nor drying step as inthe wet process is required due to the dry process, and effectivecleaning can be carried out by chemical reactions with an ozone gas,using no plasma, without giving any damages such as corrosion, etc. tosubstrates per se or cleaning reactor members such as metallic parts.

[0111] In the foregoing embodiment, the cleaning treatment was carriedout at 100° C., but a cleaning treatment temperature ranges preferablyof 20° to 350° C., which enables ruthenium etching with ozone, morepreferably a temperature range of 40° to 200° C., which ensures asatisfactory selectivity ratio of ruthenium to a resist, and mostpreferably a temperature range of 40° to 180° C.

[0112] In the foregoing embodiment, cleaning to remove rutheniumcontaminants was illustrated, but it is needless to say that an etchingtreatment of a ruthenium film on a semiconductor device with a resistformed thereon as a mask for forming a pattern can be likewise carriedout with a high throughput.

[0113] In the foregoing embodiment, ozone was used as a cleaning gas,but similar effects can be obtained with oxygen halide, nitrogen oxideand atomic oxygen, or also by supplying into the treatment chamberoxygen or nitrogen oxide excited by ultraviolet ray or plasmabeforehand. In the foregoing embodiment, a gas mixture of oxygen andnitrogen containing a few % of ozone was used, but similar effects canbe obtained when a halogen gas or a hydrogen halide gas such asfluorine, chlorine, bromine, chlorine fluoride, hydrogen fluoride,hydrogen chloride, hydrogen bromide, etc. or a reductive gas such ashydrogen, carbon monoxide, ammonia, phosphorus hydride, etc. is addedthereto.

[0114] The forementioned cleaning effect can be obtained not only incase of the ruthenium film, but also in case of a ruthenium oxide film,an osmium film and an osmium oxide film.

Example 3

[0115] An embodiment of applying the present invention to cleaning of aruthenium CVD reactor is given below:

[0116]FIG. 12 shows a ruthenium or ruthenium oxide CVD reactor.

[0117] The CVD reactor for conducting film-forming reactions comprises achamber 121, a wafer 122, a ceramic heater 123 for heating the wafer 122and a gas shower head 124 for uniformly supplying a film-forming gasonto the wafer 122. Pipes 125 for supplying or pumping the film-forminggas or a cleaning gas and the chamber 121 are heated by heaters 126 forpreventing deposition of reaction products.

[0118] The chamber 121 is provided with the gas supply pipe 125connected to an Ru (EtCp)₂ supplier 127 s for supplying Ru (EtCp)₂ upongasification as a film-forming gas [where EtCp is an abbreviation ofethylcyclopentadienyl (C₂H₅C₅H₄)], an O₂ supplier 128 s, an N₂ supplier129 s and an O₃ supplier 1210 s as a cleaning gas supplier throughvalves 127 v, 128 v, 129 v and 1210 v, respectively.

[0119] The chamber 121 is also provided with the pumping pipe 125connected to a conductance control valve 1211 for adjusting the pressurein the chamber 121 and a vacuum pump 1212.

[0120] The reactor is a cold wall type reactor, where the wafer 122 isheated to about 300° to about 750° C. by the wafer 122-mounted heater123. When the film-forming gas is used, the heater 123 is set to e.g.320° C. to obtain a film forming temperature of 300° C., whereas thechamber 121, and the pipes 125 are heated at about 150° C. by heaters126 so that the film-forming gas may not condense on the inside walls ofthe reactor 121 and pipes 125.

[0121] However, a large amount of unwanted Ru-containing reactionproducts inevitably deposit on the inside wall of the chamber 121, etc.by decomposition reaction of the film-forming gas. To obtain uniformtemperature distribution over the wafer, practically the heater size ismade larger than the wafer size, while increasing the heat input to thewafer peripheral parts of large heat escaping tendency. As a result,ruthenium or ruthenium oxide inevitably deposits on the peripheral partof the heater 123.

[0122] With repetitions of the foregoing CVD step, the deposits on theinside walls of the chamber 121 and the pipes 125 are peeled off, andthe resulting peelings whirp up by the flowing gas stream, etc. and fallonto the wafer 122 during the film forming. As a result, the peelingsfallen as particles on the wafer cause failures such as short circuits,disconnection, etc. of formed device patterns.

[0123] Effects of cleaning with ozone on particle abatement wereinvestigated in the following manners:

[0124] (1) Ruthenium film formation

[0125] At first, the inside of the chamber 121 was evacuated to a desiredegree of vacuumness and the wafer 122 was mounted on the heater 123 andthe heater 123 was set to 320° C. to maintain the temperature of thewafer 122 in a thermal equilibrium state, where the wall of the chamber121 and the pipes 125 were at about 150° C. Then, the valves 127 v and128 v were opened to supply the Ru (EtCp)₂ gas and the O₂ gas into thechamber 121, respectively, conducting formation of a 0.1 μm-thickruthenium film. The pressure in the chamber 121 was adjusted to adesired pressure by the conductance control valve 1211.

[0126] (2) Cleaning with ozone

[0127] Particle count on the film-formed wafer 122 tended to increasewhen the accumulated film thickness exceeds about 3 μm in the filmforming step when repeated in the same chamber. Thus, cleaning of thechamber 121 was conducted at every 30 runs of the film formation step.

[0128] Time allowed for the cleaning was calculated from the throughputand the rate of operation of the CVD reactor and was found to be withinabout one hour. Thus, chamber cleaning with ozone was carried out, forexample, by lowing the temperature of the heater 123 to a temperatureensuring a satisfactory etching rate, for example, 150° C., whilekeeping the temperatures of the chamber 121 and the pipes 125 with largeheat capacities as they were.

[0129] The valve 1210 v was opened to supply an ozone gas from the ozonesupplier 1210 s and the pumping rate was adjusted by the conductancecontrol valve 1211 in the same manner as in case of the film formation.The gas flow rate was 10 slm under pressure of 100 Torr.

[0130] Detection of cleaning end point was made by providing a QMSsampling point at the pumping pipe 125 and measuring changes in the ionintensity of reaction product gas generated during the cleaning fromtime to time, as shown in FIG. 13. Specifically, the time when thechange in the intensity became very small due to increasing ionintensity of RuO₄ was deemed to be a cleaning end point. In thisembodiment, ozone supply was interrupted about 20 minutes after thestart of cleaning. In this embodiment, a series of treatments wereconducted within about one hour including the time required fortemperature adjustment of the heater 123, pressure adjustment in thechamber 121, cleaning, etc.

[0131] The cleaning time could be about 20-about 30% shortened by usinga 5% ClF₃ or 5% CO-containing ozone gas, as already mentioned above.

[0132] Presupposing a case of repeating a series of such operations asruthenium film formation and cleaning with ozone, changes in particlecount on wafers 122 during the operations were measured.

[0133]FIG. 14 shows changes in particle count (particle sizes>0.3 μm),which is an average in 20-30 repetitions of film formation on 8-inchwafers. As is obvious from the results of FIG. 14, particle count on thewafers could be reduced substantially to the initial state by chambercleaning, and even if the count number is increased by successivelyconducting the film formation step, the increased count number could beagain reduced by recleaning.

[0134] As explained above, generation of particles in the chamber couldbe suppressed for a long time by conducting ozone cleaning at thespecific stages in the film formation step, whereby the ruthenium filmformation could be conducted in a stable rate.

[0135] Visual observation of the reactor inside after 20 runs ofcleaning with the ozone gas revealed that there were no metal corrosion,etc. of the chamber members.

[0136] In the foregoing embodiment, the cleaning was carried out atabout 150° C., but can be carried out at a temperature of 20° to 350°C., which enables ruthenium ething with ozone, preferably at atemperature of 40° to 200° C., which ensures a relative high rutheniumetching rate, and more preferably at a temperature of 40° to 180° C.

[0137] According to the present invention, particles within the chambercan be reduced by cleaning with an ozone gas, thereby improving theproduction yield of semiconductor devices, as mentioned above.

[0138] Furthermore, etching can be carried out without plasma and thusinside members of the chamber, that is, so called cleaning gas-suppliedparts, can be etched, and thus deposit residues within the chamber canbe much reduced, as compared with the conventional plasma cleaning.

[0139] Other oxygen halide, nitrogen oxide, atomic oxygen, etc. thanozone, or oxygen or nitrogen oxide excited by ultraviolet ray or plasmabeforehand than ozone can be supplied into the chamber as an etching gaswith the similar effect. A gas mixture of oxygen and nitrogen containinga few % of ozone further admixed with a halogen gas or a hydrogen halidegas such as fluorine, chlorine, bromine, chlorine fluoride, hydrogenfluoride hydrogen chloride, hydrogen bromide, etc. or with a reductivegas such as hydrogen, carbon monoxide, ammonia, phosphorus halide, etc.has the similar effect.

[0140] The foregoing is applied not only to the ruthenium film, but alsoto a ruthenium oxide film, an osmium film and an osmium oxide film.

Example 4

[0141] An embodiment of applying the present invention to cleaning of aruthenium etching reactor is given below:

[0142] When the etching treatment is repeated in the etching reactor,reaction products are formed by reactions between the target film to beetched or the resist film and the etching gas and deposited on thechamber inside. The deposited reaction products act as particles as incase of the CVD reactor, lowering the device production yield.

[0143] Effect of cleaning with ozone on particle abatement in theetching reactor was thus investigated.

[0144] (1) Etching of ruthenium film (pattern formation)

[0145] At first, a wafer 12 with a resist patterned on a ruthenium filmwas placed on an electrode in a chamber evacuated to a desired degree ofvacuumness, and the electrode temperature was adjusted to 20° C. Then,etching was carried out by supplying an O₂ gas, a Cl₂ gas and a N₂ gasto the chamber, while adjusting the pressure in the chamber. After theetching, the wafer 12 was transferred from the chamber, and the chamberwas evacuated again.

[0146] In this Example, cleaning with ozone was conducted at every 50runs of the wafer etching treatment in the following manner:

[0147] (2) Cleaning with ozone

[0148] As in case of the CVD reactor, the temperature of the electrodeon which the wafer was placed was set to about 100° C. during thecleaning and the cleaning was carried out for 15 minutes. A series ofthe etching steps and the cleaning step was repeated 20 times to measurechanges in particle count.

[0149] As a result, it was found that the particle count could bemaintained on a low level in the chamber by cleaning with an ozone gasand there were no corrosion, etc. on the surfaces of metallic parts inthe chamber (visual observation).

[0150] Temperature conditions for cleaning treatment, and cleaning gascomponent, etc. are not restricted to those as mentioned in theforegoing embodiment, and the cleaning rate can be improved, forexample, by adding a halogen-based gas or a reductive gas to thecleaning gas as in case of the aforementioned CVD reactor.

[0151] As explained above, chamber cleaning can be conducted for a shorttime by maintaining appropriate cleaning conditions, therebycontributing not only to improvement of stable operation for a long timeand the rate of operation of the reactor, but also to improvement ofproduction yield of devices.

[0152] While we have shown and described several embodiments inaccordance with our invention, it should be understand that thedisclosed embodiments are susceptible of changes and modificationswithout departing from the scope of the invention. Therefore, we do notintend to be bound by the details shown and described herein but intendto cover all such changes and modifications as falling within the ambitof the appended claims.

What is claimed is:
 1. A process for producing a semiconductor device,which comprises: forming a film comprising at least one member selectedfrom the group consisting of ruthenium, ruthenium oxide, osmium andosmium oxide above a semiconductor substrate; forming a mask having apattern on the film using a resist; and etching the film via the maskusing a gas comprising an atomic oxygen-donating gas.
 2. A processaccording to claim 1, wherein the atomic oxygen-donating gas is a gascontaining at least one member selected from the group consisting ofozone, oxygen halide, nitrogen oxide and atomic oxygen.
 3. A processaccording claim 1, wherein the etching is carried out by a non-plasmareaction with a gas comprising the atomic oxygen-donating gas suppliedto the film.
 4. A process according to claim 1, wherein the etching iscarried out at a treatment temperature of 20° C. to 350° C.
 5. A processfor producing a semiconductor device, which comprises: covering a filmcomprising at least one member selected from the group consisting ofruthenium, ruthenium oxide, osmium and osmium oxide, formed above asemiconductor substrate, with a resist; forming a pattern by selectivelyremoving the resist; etching the film at a first temperature; andremoving the resist at a second temperature higher than the firsttemperature.
 6. A process according to claim 5, wherein the etching andthe removing are conducted using a gas comprising an atomicoxygen-donating gas.
 7. A process according to claim 5, wherein theetching is carried out at a treatment temperature of 20° C. to 350° C.8. A process for producing a semiconductor device, which comprises:forming a film comprising at least one member selected from the groupconsisting of ruthenium, ruthenium oxide, osmium and osmium oxide, abovea substrate placed in a first treatment chamber; etching the film in asecond treatment chamber; and removing reaction products including thefilm, accumulated or deposited on surfaces of members in at least one ofthe first treatment chamber and the second treatment chamber, wherein atleast the etching or the removing of the reaction products is carriedout by using a reaction with a gas comprising an atomic oxygen-donatinggas supplied to the first treatment chamber or the second treatmentchamber.
 9. A process according to claim 8, wherein the atomicoxygen-donating gas is a gas containing at least one member selectedfrom the group consisting of ozone, oxygen halide, nitrogen oxide andatomic oxygen.
 10. A process according to claim 8, wherein the removingreaction products is carried out using a gas comprising an atomicoxygen-donating gas added with either a halogen gas, a hydrogen halidegas or a reductive gas.
 11. A process according to claim 8, wherein theremoving reaction products is carried out using a gas comprising anatomic oxygen-donating gas added with at least one member selected fromthe group consisting of fluorine, chlorine, bromine, chlorine fluoride,hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen, carbonmonoxide, ammonia and phosphorus hydride.
 12. A process according toclaim 8, wherein the etching is carried out at a treatment temperatureof 20° C. to 350° C.